Multiple-step epitaxial growth S/D regions for NMOS FinFET

ABSTRACT

A method of forming NFET S/D structures with multiple layers, with consecutive epi-SiP layers being doped at increasing dosages of P and the resulting device are provided. Embodiments include forming multiple epi-Si layers in each S/D cavity of a NFET; and performing in-situ doping of P for each epi-Si layer, wherein consecutive epi-Si layers are doped at increasing dosages of P.

TECHNICAL FIELD

The present disclosure relates to the formation of source/drain (S/D)regions by epitaxial growth (epi) for fin-type field-effect transistor(FinFET) devices. The present disclosure is particularly applicable tothe 14 nanometer (nm) technology node and beyond where epitaxial S/D isneeded.

BACKGROUND

A known approach for fabricating a 14 nm lower-power n-type field-effecttransistor (NFET) includes forming the S/D regions with a singleepi-silicon phosphorous (epi-SiP) layer that is in-situ doped with ahigh concentration of phosphorous (P), as depicted in FIG. 1. Advertingto FIG. 1 (an axiomatic view), an STI region 101 is formed between fin103 and an adjacent fin (not shown for illustrative convenience). A gatedielectric layer 105 and a gate structure 107 are then formed over thefin 103 between a high P concentration epi-SiP S/D region 109 and asecond S/D region (not shown for illustrative convenience), with spacers111 and 113 on each side of the gate structure 107. The high Pconcentration in the epi-SiP S/D region 109 is good for boosting thedirect current (DC) performance of the device. However, suchconcentrations also create an abrupt P dopant concentration transitionfrom the channel to the extension region and induce strong band to bandgeneration, both of which are a root cause of low breakdown voltage (BV)and high substrate current (Isub) in these kind of devices.

The traditional approach for solving these problems is tuning theimplant conditions to reduce the steepness of the doping profiles.However, tuning the halo/extension/pre-ion implant/S/D implantconditions without largely degrading the DC performance of the deviceresults in only a limited improvement of BV and Isub of the device.

A need therefore exists for methodology enabling formation of a graded Pdopant concentration distribution from the channel to the extensionregion of an NFET, and the resulting device.

SUMMARY

An aspect of the present disclosure is a method of forming multiple-stepepi-SiP S/D structures with consecutive epi-Si layers being doped atincreasing dosages of P.

Another aspect of the present disclosure is a method of formingmultiple-step epi-silicon carbon (epi-SiC)/epi-SiP structures withconsecutive epi-SiP layers being doped with increasing dosages of P.

A further aspect of the present disclosure is a device havingmultiple-step epi-SiP or epi-SiC/epi-SiP S/D structures with consecutiveepi-SiP layers being doped with increasing dosages of P.

Additional aspects and other features of the present disclosure will beset forth in the description which follows and in part will be apparentto those having ordinary skill in the art upon examination of thefollowing or may be learned from the practice of the present disclosure.The advantages of the present disclosure may be realized and obtained asparticularly pointed out in the appended claims.

According to the present disclosure, some technical effects may beachieved in part by a method including: forming multiple epi-Si layersin each S/D cavity of a NFET; and performing in-situ doping of P foreach epi-Si layer, wherein consecutive epi-Si layers are doped atincreasing dosages of P.

Aspects of the present disclosure include performing each of the Pdoping at a dosage of 1e18 per centimeter cubed (cm³) to 1e21/cm³. Otheraspects include forming two epi-Si layers, each layer formed to athickness of approximately one-half of a depth of each S/D cavity.Further aspects include forming three epi-Si layers, each layer formedto a thickness of approximately one-third of a depth of each S/D cavity.Another aspect includes forming an additional epi-Si layer in each S/Dcavity prior to each epi-Si layer or between each pair of epi-Si layersand performing in-situ doping of carbon (C) for each additional epi-Silayer. Additional aspects include forming two or three epi-Si layers andtwo additional epi-Si layers. Other aspects include forming eachadditional epi-Si layer to a thickness of about one half of a thicknessof each epi-Si layer. Further aspects include forming each additionalepi-Si layer to a thickness greater than or equal to 1 nm and less thana thickness of each epi-Si layer. Another aspect includes performingeach C doping and each P doping at a dosage of 1e18/cm³ to 1e21/cm³.

Another aspect of the present disclosure is a device including: a nFEThaving S/D regions, each S/D region including multiple layers ofepi-SiP, each SiP layer having a greater concentration of P than anadjacent lower SiP layer. Aspects of the device include each Si layerbeing doped with P at a dosage of 1e18/cm³ to 1e21/cm³. Other aspectsinclude two epi-SiP layers, each having a thickness of approximatelyone-half of a depth of each S/D region. Further aspects include threeepi-SiP layers, each having a thickness of approximately one-third of adepth of each S/D region. Additional aspects include an epi-SiC layerprior to each epi-SiP layer or between each pair of adjacent epi-SiPlayers. Another aspect includes two epi-SiC layers and two or threeepi-SiP layers. Other aspects include each epi-SiC layer having aminimum thickness of one nm. Further aspects include each epi-SiC layerbeing doped with C at a dosage of 1e18/cm³ to 1e21/cm³, and each epi-SiPlayer being doped with P at a dosage of 1e18/cm³ to 1e21/cm³.

A further aspect of the present disclosure is a method including:forming three epi-Si layers in each S/D cavity of a NFET, each epi-Silayer formed to a thickness of approximately one-third of a depth ofeach S/D cavity; and performing in-situ doping of P for each epi-Silayer, wherein consecutive epi-Si layers are doped at increasing dosagesof P between 1e18/cm³ to 1e21/cm³. Aspects of the present disclosureinclude forming two additional epi-Si layers in each S/D cavity, eachadditional layer formed between a pair of adjacent epi-layers and formedto a thickness of about one half of a thickness of each epi-Si layer;and performing in-situ doping of C at a dosage of 1e18/cm³ to 1e21/cm³for each additional epi-Si layer.

Additional aspects and technical effects of the present disclosure willbecome readily apparent to those skilled in the art from the followingdetailed description wherein embodiments of the present disclosure aredescribed simply by way of illustration of the best mode contemplated tocarry out the present disclosure. As will be realized, the presentdisclosure is capable of other and different embodiments, and itsseveral details are capable of modifications in various obviousrespects, all without departing from the present disclosure.Accordingly, the drawings and description are to be regarded asillustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawing and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 schematically illustrates a background epi-SiP NFET device;

FIG. 2 schematically illustrates a multi-step epi-SiP NFET device, inaccordance with an exemplary embodiment; and

FIG. 3 schematically illustrates a multi-step epi-SiC/epi-SiP NFETdevice, in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of exemplary embodiments. It should be apparent, however,that exemplary embodiments may be practiced without these specificdetails or with an equivalent arrangement. In other instances,well-known structures and devices are shown in block diagram form inorder to avoid unnecessarily obscuring exemplary embodiments. Inaddition, unless otherwise indicated, all numbers expressing quantities,ratios, and numerical properties of ingredients, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.”

The present disclosure addresses and solves the current problem of anabrupt P dopant concentration transition from the channel to theextension region of an NFET, which induces strong band to bandgeneration, low BV, and high Isub attendant upon forming NFET epi-SiPS/D regions.

Methodology in accordance with embodiments of the present disclosureincludes forming multiple epi-Si layers in each S/D cavity of a NFET. Anin-situ doping of P at increasing dosages of P from one layer to thenext is performed for each epi-Si layer.

Still other aspects, features, and technical effects will be readilyapparent to those skilled in this art from the following detaileddescription, wherein preferred embodiments are shown and described,simply by way of illustration of the best mode contemplated. Thedisclosure is capable of other and different embodiments, and itsseveral details are capable of modifications in various obviousrespects. Accordingly, the drawings and description are to be regardedas illustrative in nature, and not as restrictive.

FIG. 2 (an axiomatic view) schematically illustrates a multi-stepepi-SiP NFET device, in accordance with an exemplary embodiment.Adverting to FIG. 2, an STI region 201 is formed between fin 203 and anadjacent fin (not shown for illustrative convenience). A gate dielectriclayer 205 and a gate structure 207 are formed over fin 203 between S/Dcavity 209 and a second S/D cavity (not shown for illustrativeconvenience), with spacers 211 and 213 on each side of the gatestructure 207. Thereafter, an epi-Si layer is formed in the S/D cavity209 of the fin 203. The epi-Si layer is formed, e.g., to a thickness ofapproximately one-third of the depth of the S/D cavity 209 withapproximately 50% variation. The S/D cavity 209 for epi-SiP growth isusually ball-shaped or U-shaped with a depth, e.g., of approximately 35nm with approximately 20% of variation for current 14 nm technology. Anin-situ doping of P is performed for the epi-Si layer, e.g., at a dosageof 1e18/cm³ to 1e21/cm³, forming the epi-SiP layer 215. A second epi-Silayer is then formed, e.g., to a thickness of approximately one-third ofthe depth of the S/D cavity 209 with approximately 50% variation, overthe epi-SiP layer 215. An in-situ doping of P is performed at a dosagehigher than 1e18/cm³, but less than or equal to 1e21/cm³, forming theepi-SiP layer 217. A third epi-Si layer is then formed, e.g., to athickness of approximately one-third of the depth of the S/D cavity 209with approximately 50% variation, over the epi-SiP layer 217. An in-situdoping of P is performed at a dosage greater than or equal to theepi-SiP layer 217, e.g., less than or equal to 1e21/cm³, forming theepi-SiP layer 219. The thickness of each epi-SiP layer may increase fromthe bottom to the top of the S/D cavity 209 as the P concentrationincreases.

Although three epi-SiP layers, e.g., epi-SiP layers 215, 217, and 219,are formed in FIG. 2, two epi-SiP layers (not shown for illustrativeconvenience) could alternatively be formed in the S/D cavity 209. Whentwo epi-SiP layers are formed, each epi-Si layer is formed, e.g., to athickness of approximately one-half of the depth of the S/D cavity 209with 50% of variation, and each consecutive epi-Si layer is doped with adosage of P greater than the previous layer, but still between 1e18/cm³and 1e21/cm³.

FIG. 3 (an axiomatic view) schematically illustrates a multi-stepepi-SiC/epi-SiP NFET device, in accordance with another exemplaryembodiment. FIG. 3 is similar to FIG. 2; however, instead of three ortwo consecutive epi-Si layers doped with P, an additional epi-Si layerdoped with C may be added between each pair of adjacent epi-SiP layers.Adverting to FIG. 3, an STI region 301 is formed between fin 303 and anadjacent fin (not shown for illustrative convenience). A gate dielectriclayer 305 and a gate structure 307 are formed over fin 303 between S/Dcavity 309 and a second S/D cavity (not shown for illustrativeconvenience), with spacers 311 and 313 on each side of the gatestructure 307. Thereafter, an epi-Si layer is formed in the S/D cavity309 of the fin 303. The epi-Si layer is formed, e.g., to a thicknessslightly greater than one-fifth of the depth of the S/D cavity 309 with50% variation. An in-situ doping of P is performed, e.g., at a dosageequal to or greater than 1e18/cm³ and less than 1e21/cm³, forming theepi-SiP layer 315. Next, a second epi-Si layer is formed, e.g., to athickness of approximately one-half of the thickness of the epi-SiPlayer 315 with 50% variation, e.g., a thickness greater than or equal to1 nm and less than the thickness of the epi-SiP layer 315. An in-situdoping of C is performed, e.g., at a dosage of 1e18/cm³ to 1e21/cm³,forming the epi-SiC layer 317. A third epi-Si layer is then formed overthe epi-SiC layer 317, e.g., to a thickness approximately the same asthe thickness of the epi-SiP layer 315. An in-situ doping of P isperformed at a concentration higher than the dosage of the epi-SiP layer315, e.g., at dosage greater than 1e18/cm³ and less than 1e21/cm³,forming the epi-SiP layer 319. Thereafter, epi-SiC layer 321 and epi-SiPlayer 323 are formed in the same manner as epi-SiC layer 317 and epi-SiPlayer 319, respectively; however, the in-situ doping for the epi-SiPlayer 323 is at a greater P dopant concentration than for the epi-SiPlayer 319, e.g., greater than 1e18/cm³ and less than or equal to1e21/cm³. Again, the thickness of each epi-SiP layer may increase fromthe bottom to the top of the S/D cavity 309 as the P concentrationincreases. In this instance, the epi-SiC layers 317 and 321 are doped atapproximately the same dosage of C, e.g., 1e18/cm³ to 1e21/cm³.

Although an in-situ doping of P is performed with respect to the firstepi-Si layer formed in the S/D cavity 309, e.g., epi-SiP layer 315, inFIG. 3, the first epi-SiP layer may alternatively be eliminated, makingthe epi-SiC layer 317 first. However, regardless of whether the firstepi-Si layer formed in the S/D cavity 309 is in-situ doped with P or C,the last epi-Si layer formed in the S/D cavity 309 must be in-situ dopedwith P.

The embodiments of the present disclosure can achieve several technicaleffects including achieving a graded P dopant distribution from thechannel to the extension region of an NFET and thereby increase BV anddecrease Isub of the device. Embodiments of the present disclosure enjoyutility in various industrial applications as, for example,microprocessors, smart phones, mobile phones, cellular handsets, set-topboxes, DVD recorders and players, automotive navigation, printers andperipherals, networking and telecom equipment, gaming systems, anddigital cameras. The present disclosure therefore has industrialapplicability in 14 nm technology node devices and beyond whereepitaxial S/D is needed.

In the preceding description, the present disclosure is described withreference to specifically exemplary embodiments thereof. It will,however, be evident that various modifications and changes may be madethereto without departing from the broader spirit and scope of thepresent disclosure, as set forth in the claims. The specification anddrawings are, accordingly, to be regarded as illustrative and not asrestrictive. It is understood that the present disclosure is capable ofusing various other combinations and embodiments and is capable of anychanges or modifications within the scope of the inventive concept asexpressed herein.

What is claimed is:
 1. A method comprising: forming multiple epitaxiallygrown (epi) silicon (Si) layers in each source/drain (S/D) cavity of an-type field effect transistor (NFET); performing in-situ doping ofphosphorous (P) for each epi-Si layer, wherein consecutive epi-Si layersare doped at increasing dosages of P, wherein two epi-Si layers areformed, each layer formed to a thickness of approximately one-half of adepth of each S/D cavity.
 2. The method according to claim 1, comprisingperforming each of the P doping at a dosage of 1e18 per centimeter cubed(cm³) to 1e21/cm³.
 3. The method according to claim 1, furthercomprising: forming an additional epi-Si layer in each S/D cavity priorto each epi-Si layer or between each pair of epi-Si layers andperforming in-situ doping of carbon (C) for each additional epi-Silayer.
 4. The method according to claim 3, comprising forming two orthree epi-Si layers and two additional epi-Si layers.
 5. The methodaccording to claim 3, comprising forming each additional epi-Si layer toa thickness of about one half of a thickness of each epi-Si layer. 6.The method according to claim 3, comprising forming each additionalepi-Si layer to a thickness greater than or equal to 1 nanometer (nm)and less than a thickness of each epi-Si layer.
 7. The method accordingto claim 3, comprising performing each C doping and each P doping at adosage of 1e18 per centimeter cubed (cm³) to 1e21/cm³.
 8. A methodcomprising: forming three epitaxially grown (epi) silicon (Si) (epi-Si)layers in each source/drain (S/D) cavity of a n-type field effecttransistor (NFET), each epi-Si layer formed to a thickness ofapproximately one-third of a depth of each S/D cavity; and performingin-situ doping of phosphorous (P) for each epi-Si layer, whereinconsecutive epi-Si layers are doped at increasing dosages of P between1e18 per centimeter cubed (cm³) to 1e21/cm³.
 9. The method according toclaim 8, further comprising: forming two additional epi-Si layers ineach S/D cavity, each additional layer formed between a pair of adjacentepi-layers and formed to a thickness of about one half of a thickness ofeach epi-Si layer; and performing in-situ doping of carbon (C) at adosage of 1e18 per centimeter cubed (cm³) to 1e21/cm³ for eachadditional epi-Si layer.